But you can't route MACs... you can't associate domain names to MACs...
Maybe for a LAN that's fine, but for connecting devices between broadcast domains, it just doesn't cut it.
Maybe for a LAN that's fine, but for connecting devices between broadcast domains, it just doesn't cut it.
Because else you need ARP, IP, UDP, TCP, etc.
I'm certain there are reasons IP came to live alongside/on top of MAC, but saying you can't do multi-hop routing with it just isn't true. If all the technologies of the Internet were reset tomorrow, how might you design the perfect layer 2 addressing and routing system?
It just isn’t suitable for this.
AB:33:C6:C6:19:74
I used a MAC address generator to get those two, but I think two is enough to make the discussion. Current reality aside, would you be able to identify those with binary math as being on the same network device, different network devices, across the world? MAC addresses on physical NICs are provided by the manufacturer, sure you can adjust them but I think that leaves the good-faith portion of this discussion.
So if you wanted to have those to communicate no matter what you would have to have a network device state: "I'm network device A, I have this device 0C:F9:31:D2:DB:51" then another state: "I'm network device B, I have this device AB:33:C6:C6:19:74". Then whenever 0C:F9:31:D2:DB:51 wants to talk with AB:33:C6:C6:19:74 it's network device will have to just send it to the next upstream network device or if there are multiple network devices that could be upstream you could send it to them all which is just not great for security whatsoever or you now have to do a recursive lookup for whatever n devices might yet be upstream and wait for a response to see if one of those has it. Overall trying to send ethernet frames globally without an IP network sounds like not a great idea.
Still, there's doesn't seem to be any reason you couldn't just say "device 1 gets MAC 00:00:00:00:00:01" and "device 2 gets 00:00:00:00:00:02" and the gateway controller gets :::00 and there's a special address on :::FF that can be used to talk to everyone...
Is that it? Is that all there is to IP? A loose pattern for reducing search scope, a couple reserved addresses for special cases, and a balance between address bitsize and total number of unique addresses (without requiring additional routing complexity)?
It all seems so... simple
> It all seems so... simple
Because you haven’t even thought through basic use cases.
Then you realize doing some action ends up being O(n^2) so you add some workaround in your switch and cache some things. And you know what they say about cache invalidation. And vendor A implemented it wrong in 1993 so you have a special case for their systems. And then you want to handle abuse cases. And authentication. And you're competing against the whole rest of the world and your thing isn't enough better.
The reason we don't is because at the time IP was introduced, there were many alternative physical layers in active use. And while Ethernet is near ubiquitous now, what we learnt from that was that it is unreasonable to assume that all your data will go over the same physical layer. And so you need a standard addressing format that will work elsewhere too.
Nothing stops you from stripping it back locally and using MAC addresses for everything internal to you, and ditching IP, and "just" gateway to/from IP. Lots of people did gateway between different protocols before IP became the dominant choice.
But you won't get everyone else to change because it'd require new firewall and new routers, and all kinds of software rewrites, and you can see how long the IPv6 transition has taken, so you'd still need to wrap and unwrap TCP/IP and find a way to address IP for everything that isn't 100% local, and even for lots of local-only stuff unless you want to rewrite everything.
There would be potential ways. E.g. you could certainly use a few bits to say "this is external" and then have some convention to pack an IPv4 address into the MAC or let an IPv6 address overflow into the data, and use that to make gatewaying and routing to external networks easier, while everything else just relies on the MAC. But you'd still need a protocol header for other things too, and then the question is how much benefit you would gain from ditching pretty much just ARP, which isn't exactly complex, a lookup table, and replacing the IPs in the header with just a destination MAC. Because the rest of the complexity is still there.
And you can gain most of the benefit of that by getting an IPv6 EUI64 address [1]. They'll work with "normal" IP equipment, and you can optimize in your own software by having the IP stack ditch ARP lookups when they see a local EUI64 address. Whether that optimisation actually makes a difference is another question.
[1] https://community.cisco.com/t5/networking-knowledge-base/und...
The table required for the whole Internet is large, but not gigabytes.
You can't route by MAC-address because it's effectively random. You'd have to store the port number for every device separately. This works fine at LAN scale, but not for the whole Internet.
Not that I see any advantages to the approach but it's almost workable(?), if a little silly, at internet scale:
If every device had a 64byte ID, guesstimating 10billion people * 100 devices/head gets us a 'measly' 64TB of storage. Double that to include routing info gets us to ~128TB. A bit much to be practical, but not entirely insane either.
Question: how does dns lookup differ from MAC lookup. Why is domain name lookup feasible, but not MAC?
a central lookup database for mac addresses (which could be distributed by having separate servers for a segment of the address space) doesn't make much sense because the distance of a server to the location of the device is to great and would make updates expensive.
so the router has to remember each address used. but at least it would not have to store all addresses in existence. actually, i think the storage needs are similar to those for NAT. well, except backbone routers which have to store a lot more.
the actual problem is the initial discovery of a MAC address. where does the routing information for a MAC address come from?
you need some peer finding protocols like DHT, and those are slower.
and i think the self assigning protocol in link-local could even go a step further. instead of hard coding a subnet, it could detect the subnet by copying the one from its nearest neighbor. so start with a random address, talk to neighbor to learn the subnet (and netmask) in use and switch to a new address within that subnet. then possibly run DHCP and update the address again. for static addresses DHCP could identify hosts by its cryptographic host key (like the one for SSH)
when two subnets join one of them may have to adjust its prefix. more complex, but still possible.
subnet prefixes could still be assigned to organizations to avoid overlap on a global level.
i am sure i am missing some details but i think in general this could work.
It works on small scales. We can stitch together a few LANs with ethernet switches. The switches initially forward everything to all ports, but learn where the MACs are so as to send frames only to ports where the destination MAC is known to be.
Ethernet switching won't scale to anywhere near the complexity of the Internet.
There were different teams/universities working on what today we would call LAN and WAN. I forget the details and history (I'm sure someone here, who was involved, could chime in, hah) and might have this wrong, but the result is LAN networking is MAC based while WAN networking is IP based.
It's one of those accidents of history that things are just the way they are and many don't question it. I run into it a lot describing basic networking concepts or early cisco material when people ask _why_ both MACs and IP addresses exist and its just... not always the correct time to explain those details to them.
- "Directly connected/visibile" means node X can contact node Y simply by throwing something on the medium (wire, radio, etc.) and doesn't have to knowingly send to a middleman (router).
When Ethernet was invented in the early 80's there were a lot more L2 technologies. Most are uncommon now (Frame Link DLCIs I think fall in this category, and PPP/dialup was common at one time - no MACs there) except for one: I don't think the cellular network uses MAC addresses at all. I could be wrong with newer 4G/5G stuff which overlaps with Wi-Fi in various places.